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Abstract:

In the field of vehicle occupant detectors there is a need for an
improved vehicle occupant detector which is able to consistently identify
the number of occupants in vehicles having windscreens with different
infrared transmission characteristics. A vehicle occupant detector
comprises a first infrared illuminator that is operable at a first
infrared wavelength to illuminate an interior of a vehicle, and a second
infrared illuminator that is operable at a second infrared wavelength to
illuminate an interior of a vehicle. The vehicle occupant detector also
includes a first infrared detector to capture a first image of the
interior of the vehicle illuminated at the first infrared wavelength, and
a second infrared detector to capture a second image of the interior of
the vehicle illuminated at the second infrared wavelength. The first and
second infrared detectors have the same infrared detection
characteristics.

Claims:

1. A vehicle occupant detector comprising: a first infrared illuminator
operable at a first infrared wavelength to illuminate an interior of a
vehicle; a second infrared illuminator operable at a second infrared
wavelength to illuminate an interior of a vehicle; a first infrared
detector to capture a first image of the interior of the vehicle
illuminated at the first infrared wavelength; and a second infrared
detector to capture a second image of the interior of the vehicle
illuminated at the second infrared wavelength, the first and second
infrared detectors having the same infrared detection characteristics.

2. A vehicle occupant detector according to claim 1 wherein the first and
second infrared detectors are two identical, separate detector units.

3. A vehicle occupant detector according to claim 1 wherein the first and
second infrared detectors occupy discrete portions of a single detector
unit.

4. A vehicle occupant detector according to claim 3 wherein the single
detector unit includes a first group of pixels defining the first
infrared detector and a second group of pixels defining the second
infrared detector.

5. A vehicle occupant detector according to claim 4 wherein the pixels in
the first group lie diagonally adjacent to one another and the pixels in
the second group lie diagonally adjacent to one another and adjacent to
the pixels in the first group.

6. A vehicle occupant detector according to claim 4 wherein the pixels in
the first group lie in one half of the single detector unit and the
pixels in the second group lie in the other half of the single detector
unit.

7. A vehicle occupant detector according to claim 6 wherein the halves of
the single detector unit lie, in use, above and below one another.

8. A vehicle occupant detector according to claim 1 further including a
processing module to: determine the ratio of detected infrared in
corresponding areas of the first and second images; and identify human
skin in a respective area when the ratio of detected infrared in the said
respective area lies within a desired range.

9. A vehicle occupant detector according to claim 1 wherein the first
infrared wavelength lies in the range 1400 nm to 1600 nm and the second
infrared wavelength lies in the range 1000 nm to 1200 nm.

10. A method of detecting one or more occupants in a vehicle comprising
the steps of: (a) illuminating an interior of the vehicle at a first
infrared wavelength; (b) illuminating the interior of the vehicle at a
second infrared wavelength; (c) capturing a first image of the interior
of the vehicle illuminated at the first infrared wavelength with a first
infrared detector; and (d) capturing a second image of the interior of
the vehicle illuminated at the second infrared wavelength with a second
infrared detector, the first and second infrared detectors having the
same infrared detection characteristics.

11. A method of detecting one or more occupants in a vehicle according to
claim 10 further including the steps of: (e) determining the ratio of
detected infrared in corresponding areas of the first and second images;
and (f) identifying human skin in a respective area when the ratio of
detected infrared in the said respective area lies within a desired
range.

12. A method of detecting one or more occupants in a vehicle according to
claim 11 wherein determining the ratio of detected infrared in
corresponding areas of the first and second images includes determining
the ratio of detected infrared in corresponding pixels of the first and
second images, and identifying human skin in a respective area includes
identifying human skin in a respective pixel when the ratio of detected
infrared in the said respective pixel lies within a desired range.

13. (canceled)

14. (canceled)

Description:

[0001] This invention relates to a vehicle occupant detector and a method
of identifying one or more occupants in a vehicle.

[0002] It is known from WO 2008/099146 to provide a vehicle occupant
detector which includes first and second infrared illuminators to
illuminate the interior of a vehicle at different infrared wavelengths.
According to WO 2008/099146 a first preferred infrared wavelength lies in
the range 1400 nm to 1600 nm while a second preferred infrared wavelength
lies in the range 800 nm to 900 nm.

[0003] The vehicle occupant detector known from WO 2008/099146 also
includes first and second infrared detectors to capture respective images
of the interior of the vehicle within each of the first and second
preferred ranges of infrared wavelengths.

[0004] WO 2008/099146 teaches that the first infrared detector should be
an infrared camera while the second infrared detector should be a silicon
video camera capable of capturing an image within the wavelength range of
300 nm to 1000 nm.

[0005] The inclusion of a video camera as a second infrared detector
reduces the cost of the vehicle occupant detector, while operating in the
lower infrared frequency range of 800 nm to 900 nm provides a good
contrast between the extent to which human skin reflects infrared in this
range and the extent to which other organic/inorganic materials (e.g.
cabbages, plastics, clothing) reflect infrared in this range.

[0006] WO 2008/099146 indicates that good contrast between the infrared
reflection characteristics of human skin and such other organic/inorganic
materials is important so that the vehicle occupant detector can
distinguish between such materials when seeking to detect the number of
occupants in a vehicle.

[0007] However, one drawback with the vehicle occupant detector of WO
2008/099146 is that it has difficulty consistently identifying the number
of occupants in vehicles having windscreens with differing infrared
transmission characteristics. Since the transmission characteristics of a
windscreen can vary according to the make and model of vehicle, as well
as when the vehicle was manufactured, this inconsistency means that the
vehicle occupant detector of WO 2008/099146 is wholly unsuitable for a
practical application in which the windscreen of each successive vehicle
observed potentially has a different infrared transmission
characteristic.

[0008] There is, therefore, a need for an improved vehicle occupant
detector that is able to consistently identify the number of occupants in
a full range of vehicles having windscreens with differing infrared
transmission characteristics.

[0009] According to a first aspect of the invention there is provided a
vehicle occupant detector comprising:

[0010] a first infrared
illuminator operable at a first infrared wavelength to illuminate an
interior of a vehicle;

[0011] a second infrared illuminator operable at a
second infrared wavelength to illuminate an interior of a vehicle;

[0012]
a first infrared detector to capture a first image of the interior of the
vehicle illuminated at the first infrared wavelength; and

[0013] a second
infrared detector to capture a second image of the interior of the
vehicle illuminated at the second infrared wavelength,

[0014] the first
and second infrared detectors having the same infrared detection
characteristics.

[0015] The inclusion of first and second infrared detectors having the
same detection characteristics eliminates any differences in the first
and second images arising from the manner in which the scattered infrared
is detected, and so minimises the effect that varying infrared
transmission characteristics from one windscreen to another has on the
captured images. Eliminating such detection differences helps the vehicle
occupant detector of the invention to consistently identify human
occupants irrespective of the windscreen type in the vehicle.

[0016] Optionally the first and second infrared detectors are two
identical, separate detector units. Such an arrangement ensures that the
first and second infrared detectors have the same detection
characteristics while providing flexibility in the relative arrangement
of the two detectors.

[0017] Preferably the first and second infrared detectors occupy discrete
portions of a single detector unit. The inclusion of a single detector
unit ensures consistency in the performance of the two infrared detectors
while significantly reducing the cost of producing the vehicle occupant
detector.

[0018] The single detector unit may include a first group of pixels
defining the first infrared detector and a second group of pixels
defining the second infrared detector. Such an arrangement provides a
ready way of detecting first and second infrared wavelengths using a
single detector unit.

[0019] In a preferred embodiment of the invention the pixels in the first
group lie diagonally adjacent to one another and the pixels in the second
group lie diagonally adjacent to one another and adjacent to the pixels
in the first group. Arranging the pixels in this manner allows use of the
whole detector unit for detecting the infrared wavelengths.

[0020] Optionally the pixels in the first group lie in one half of the
single detector unit and the pixels in the second group lie in the other
half of the single detector unit.

[0021] The halves of the single detector unit may lie, in use, above and
below one another.

[0022] Such features allow the shape of each of the first and second
groups of pixels to correspond to the typical aspect ratio, i.e. shape,
of a vehicle windscreen.

[0023] In another preferred embodiment of the invention the vehicle
occupant detector further includes a processing module to:

[0024]
determine the ratio of detected infrared in corresponding areas of the
first and second images; and

[0025] identify human skin in a respective
area when the ratio of detected infrared in the said respective area lies
within a desired range.

[0026] The inclusion of such a processing module allows the vehicle
occupant detector to determine the ratio of detected infrared in
corresponding areas of the first and second images. Changes in infrared
transmission characteristics from one windscreen to another have a
similar effect on each of the first and second infrared wavelengths and
so the determined ratio will be largely unaffected by such changes. As a
result the ability of the vehicle occupant detector to identify human
skin is unaffected by changes in windscreen infrared transmission
characteristics and so the vehicle occupant detector is even more able
consistently to identify human occupants in a vehicle.

[0027] In a further preferred embodiment of the invention the first
infrared wavelength lies in the range 1400 nm to 1600 nm and the second
infrared wavelength lies in the range 1000 nm to 1200 nm.

[0028] Utilising a second infrared wavelength in the range 1000 nm to 1200
nm reduces the contrast between the infrared reflection characteristics
of human skin and organic materials because human skin reflects less
infrared at this wavelength. However, moving the second range of infrared
wavelengths closer to the first range of infrared wavelengths, than is
the case in known vehicle occupant detectors, reduces still further any
difference in the effect that changes in infrared transmission
characteristics from one windscreen to another have on the first and
second wavelengths. Consequently the vehicle occupant detector is further
isolated from the differing effects on infrared transmission of different
windscreens, and so the consistency with which the vehicle occupant
detector is able to identify human occupants in a vehicle is further
improved.

[0029] According to a second aspect of the invention there is provided a
method of detecting one or more occupants in a vehicle comprising the
steps of:

[0030] (a) illuminating an interior of the vehicle at a first
infrared wavelength;

[0031] (b) illuminating the interior of the vehicle
at a second infrared wavelength;

[0032] (c) capturing a first image of
the interior of the vehicle illuminated at the first infrared wavelength
with a first infrared detector; and

[0033] (d) capturing a second image
of the interior of the vehicle illuminated at the second infrared
wavelength with a second infrared detector,

[0034] the first and second
infrared detectors having the same infrared detection characteristics.

[0035] Optionally detecting one or more occupants in a vehicle further
includes the steps of:

[0036] (e) determining the ratio of detected
infrared in corresponding areas of the first and second images; and

[0037] (f) identifying human skin in a respective area when the ratio of
detected infrared in the said respective area lies within a desired
range.

[0038] In a preferred embodiment of the invention determining the ratio of
detected infrared in corresponding areas of the first and second images
includes determining the ratio of detected infrared in corresponding
pixels of the first and second images, and identifying human skin in a
respective area includes identifying human skin in a respective pixel
when the ratio of detected infrared in the said respective pixel lies
within a desired range.

[0039] The method of the invention shares the advantages of the
corresponding features of the vehicle occupant detector of the invention.

[0040] There now follows a brief description of a preferred embodiment of
the invention, by way of non-limiting example, with reference being made
to the accompanying drawings in which:

[0041] FIG. 1 illustrates schematically how the extent to which various
materials reflect electromagnetic radiation varies according to the
wavelength of the electromagnetic radiation;

[0042] FIG. 2 shows a schematic view of a vehicle occupant detector
according to a first embodiment of the invention;

[0043] FIG. 3(a) shows a first arrangement of first and second groups of
pixels in an infrared detector unit;

[0044] FIG. 3(b) shows a second arrangement of first and second groups of
pixels in an infrared detector unit;

[0045] FIG. 4(a) illustrates schematically first and second images
captured through a first windscreen;

[0046] FIG. 4(b) illustrates schematically first and second images
captured through a second windscreen having different infrared
transmission characteristics to the first windscreen; and

[0048] A vehicle occupant detector according to a first embodiment of the
invention is designated generally by the reference numeral 10.

[0049] The vehicle occupant detector 10 includes a first infrared
illuminator 12 which operates at a first infrared wavelength of 1550 nm.
Other embodiments of the invention (not shown) may include a first
infrared illuminator 12 that operates at an infrared wavelength in the
range 1400 nm to 1600 nm.

[0050] The vehicle occupant detector 10 also includes a second infrared
illuminator 14 which operates at 1050 nm. Other embodiments of the
invention (not shown) may include a second infrared illuminator 14 that
operates at an infrared wavelength in the range 1000 nm to 1200 nm, and
still further embodiments of the invention may include one or more
infrared illuminators that operate over a still further extended range.

[0051] Each of the first and second infrared illuminators 12, 14 is a
laser.

[0052] In addition, the vehicle occupant detector 10 includes first and
second infrared detectors 16, 18.

[0053] The first infrared detector 16 is arranged to capture a first image
20 of the interior of a vehicle 19 illuminated at the first infrared
wavelength of 1550 nm, as shown schematically, for example, in FIGS. 4(a)
and 4(b).

[0054] The second infrared detector 18 is arranged to capture a second
image 22 of the interior of a vehicle 19 illuminated at the second
infrared wavelength of 1050 nm, as also shown schematically in FIGS. 4(a)
and 4 (b).

[0055] Each of the first and second infrared detectors 16, 18 have the
same detection characteristics, i.e. each reacts to incident infrared
radiation in the same way.

[0056] In the embodiment shown the first and second infrared detectors 16,
18 occupy discrete portions of a single detector unit 24. In particular,
the single detector unit 24 includes first and second groups of pixels
26, 28 which respectively define the first and second infrared detectors
16, 18.

[0057] First pixels 30 in the first group of pixels 26 lie diagonally
adjacent to one another and second pixels 32 in the second group of
pixels 28 lie diagonally adjacent to one another and adjacent to the
first pixels 30, as shown in FIG. 3(a).

[0058] In such an arrangement the detector unit 24 may include a filter
34, e.g. a narrow bandpass filter, configured to allow the transmission
of only the first infrared wavelength (1550 nm) into each of the first
pixels 30 and the transmission of only the second infrared wavelength
(1050 nm) into the second pixels 32. Such a configuration means that the
or each of the first and second pixels 30, 32 receives only the active
illumination wavelength to maximise the contrast between human skin and
surrounding materials.

[0059] The vehicle occupant detector is configured to generate separate
first and second images 20, 22 of the interior of the vehicle from the
data collected by the respective first and second groups of pixels 26, 28
by interpolating between adjacent pixels 30, 32 in each group 26, 28.

[0060] A suitable single detector unit 24 is a single Indium Gallium
Arsenide (InGaAs) detector.

[0061] In other embodiments of the invention the first pixels 30 may lie
in one half of the detector unit 24, the second pixels 32 lie in the
other half of the detector unit 24, and the respective halves lie one
above the other, as shown in FIG. 3(b). Such an arrangement allows, e.g.
the upper half 36 of the detector unit 24 to capture the first image 20
of the interior of a vehicle at the first infrared wavelength, and the
lower half 38 to capture the second image 22 of the interior of the
vehicle at the second infrared wavelength.

[0062] In still further embodiments of the invention (not shown) the first
and second infrared detectors 16, 18 may be two identical, separate
detector units.

[0063] The vehicle occupant detector 10 shown also includes a processing
module 40 to determine the ratio of detected infrared in corresponding
areas of the first and second images 20, 22, and to identify human skin
in a respective area when the ratio of detected infrared in the said
respective area lies within a desired range.

[0064] In particular, the processing module 38 determines the ratio of
detected infrared in corresponding pixels 30, 32 of the first and second
images 20, 22, and identifies human skin in a respective pixel 30, 32
when the ratio of detected infrared in the said respective pixel 30, 32
lies within a desired range.

[0065] The desired range may be less than or greater than a predetermined
threshold, or determined in some other manner.

[0066] In other embodiments of the invention, the processing module 40 may
identify human skin a respective area by performing a different
arithmetic operation or a logical operation on the infrared detected in
the said respective area of the first and second images 20, 22.

[0067] In use, the first infrared detector 16, i.e. the first group of
pixels 26 in the detector unit 24, captures a first image 20 of the
interior of a first vehicle which is illuminated at the first infrared
wavelength of 1550 nm, as shown schematically in FIG. 4(a).

[0068] As illustrated schematically in FIG. 1, both human skin and green
organic matter exhibit low reflectance of infrared at this wavelength,
and so each of a human head 42 and a green organic object, such as a
cabbage 44, appear dark in the image 20 because only low levels of the
incident infrared radiation (at a wavelength of 1550 nm) are scattered
back to the first infrared detector 16. In particular, at a wavelength of
1550 nm water in human skin is highly absorbing of infrared and
predominates over other skin constituents, as illustrated schematically
in FIG. 5.

[0069] In the meantime synthetic materials 46 in the interior of the
vehicle exhibit a greater degree of reflectance than human skin and green
organic matter, and so appear light in the image 20 because more of the
incident infrared radiation (at a wavelength of 1550 nm) is reflected.

[0070] At the same time the second infrared detector 18, i.e. the second
group of pixels 26 in the detector unit 24, captures a second image 22 of
the interior of the vehicle which is illuminated at the second infrared
wavelength of 1050 nm.

[0071] At this wavelength human skin exhibits greater reflectance than
green organic matter, as do synthetic materials, and so the human head 42
and synthetic materials 46 appear light in the second image, while the
cabbage 44 continues to appear dark. In particular, at a wavelength of
1050 nm haemoglobin (Hb and HbO2) and melanin in human skin reflect more
infrared than they do at, say 808 nm, and so predominate, even though
water in human skin absorbs more infrared at 1050 nm than it does at, say
808 nm, as illustrated schematically in FIG. 5.

[0072] The processing module 40 then determines the ratio of detected
infrared in corresponding pixels of the first and second images 20, 22
and identifies human skin in a respective pixel 30, 32 when the ratio of
detected infrared in the said respective pixel 30, 32 lies within a
desired range.

[0073] For example, the processing module 40 establishes the amount of
reflected infrared at the first wavelength of 1550 nm detected at a given
pixel 48 in the first image 20 and the amount of reflected infrared at
the second wavelength of 1050 nm at the same given pixel 48 in the second
image 22.

[0074] The processing module 40 may then determine the ratio of detected
infrared at this pixel 48 by dividing the detected amount of reflected
first wavelength infrared by the detected amount of reflected second
wavelength infrared to arrive at a first ratio value R1.

[0075] If this first ratio value R1 is, e.g. smaller than, a
predetermined threshold value then the processing module 40 identifies
the given pixel 48 as relating to human skin.

[0076] Depending on the number and arrangement of adjacent pixels which
have been determined to relate to human skin the processing module 40 is
able to identify a human head, and hence a vehicle occupant.

[0077] FIG. 4(b) illustrates schematically similar captured first and
second images 20, 22 from a second vehicle which has a windscreen with
different infrared transmission characteristics to the windscreen in the
first vehicle and in particular, a windscreen that is a poorer
transmitter of infrared than the windscreen of the first vehicle.

[0078] As shown in FIG. 4(b), the first and second infrared wavelengths
are scattered by each of the elements of interest, i.e. human skin,
organic material and synthetic materials, in a similar relative manner as
in the first vehicle.

[0079] However, the windscreen of the second vehicle inhibits the
transmission of infrared radiation, and so attenuates the amount of
reflected infrared radiation that reaches the first and second infrared
detectors 16, 18.

[0080] Nevertheless, because the first and second infrared detectors 16,
18 have the same detection characteristics, and because the first and
second infrared wavelengths are relatively close to one another in the
electromagnetic spectrum, the windscreen attenuation has an essentially
uniform effect on the first and second images 20, 22.

[0081] Consequently, the relative amount of reflected infrared radiation
detected in a given pixel 48 in each image 20, 22, and hence the ratio
R2 of detected infrared in each image 20, 22, remains essentially
the same. Accordingly, since R2 essentially equals R1, the
vehicle occupant detector 10 is able to discern human skin in the same
manner as with the first vehicle, despite the differing infrared
transmission characteristics of the windscreen in the second vehicle. The
vehicle occupant detector is, therefore, able to consistently identify
vehicle occupants irrespective of the nature of the windscreen in a
vehicle.